64 Audio Solo Planar Magnetic IEM

64 Audio’s Solo expertly covers the entire sonic spectrum with a single planar driver. As the final note in their legendary tia™ line of UIEMs, Solo has been years in the making. Staying true to the tech-disruptive legacy of Fourté, Trio, and Duo, 64 Audio looked to the past for innovative solutions to the modern challenge of tuning a single driver.

In addition to a traditional electronic filter that subtly shifts the tonal balance, 64 Audio introduced the world’s first Helmholtz resonator in an IEM. The 14.2mm planar driver’s acoustic chamber integrates two Helmholtz resonators, meticulously tuned to acoustically sculpt its frequency response. This chamber is also engineered to include their apex core design, expertly relieving pneumatic pressure and enhancing the sense of physical space to a degree never before experienced in a single-driver IEM. Combined with their patented LID technology, all of these innovations are housed in their most striking design update since the introduction of Fourté in 2016. These elements unite to deliver a sound that is quintessentially 64 Audio, combining the exceptionally detailed transient response of planar technology with an unexpectedly robust low-frequency presence.

As 64 Audio’s first single-driver UIEM, Solo achieves what Fourté did in 2016 when they simultaneously unveiled the world’s first 18-driver IEM and offered a four-driver alternative that arguably provided more sonic resolution. By accomplishing this with a single driver, 64 Audio opens a new realm of possibilities in micro-acoustic design.

The planar magnetic driver features a flat diaphragm with embedded conductors suspended between two sets of magnets, unlike traditional dynamic drivers that utilize a conical diaphragm driven by a voice coil. Because the entire diaphragm moves uniformly due to the planar magnetic field, 64 Audio can deliver the detail and micro-transient information that would typically require a dedicated high-frequency driver. Since the diaphragm isn’t driven by a voice coil attached to a cone, which can cause uneven movement, 64 Audio can reliably extract a true high-resolution full range sound from this single driver.

64 Audio has long recognized the presence of planar magnetic technology in portable hi-fi, but aimed to truly showcase its potential in their products. To offer a new perspective on this technology, 64 Audio needed a combination of a slight but broad reduction in high-frequency amplitude and the attenuation of a few very narrow frequency bands. As the electronic filter acts as a very subtle reductive shelf, they had to think creatively to effectively control some problematic frequencies. For this, 64 Audio drew on their years of research into Helmholtz resonators, an acoustic device from the mid-19th century. The two micro-cavities, 3D printed into Solo’s sound chamber, operate by forcing air in and out, causing the air inside to resonate at a specific frequency. By precisely determining the dimensions of the cavity and its neck, 64 Audio can target a very narrow resonant frequency to amplify or diminish.

Linear Impedance Design (LID) is a patented circuit that compensates for the non-linear electrical resistance resulting from Solo’s electronic shelf filter. Variations in source amplifier output impedance in devices like smartphones, body packs, DAC/amps, and DAPs typically lead to changes in frequency response. LID restores proper interaction with the source, preserving the intended sound signature and ensuring consistent, reliable performance.

Adding to their list of innovations, 64 Audio implements their patented pressure-relieving technology in the form of apex core, elevating this design to new levels of fidelity and spatial acuity. Because Solo’s acoustic chamber includes 64 Audio’s integrated apex core technology, they achieve a similar fit and comfort to that of the Duo. The design offers just enough isolation to allow the listener to focus on the audio while feeling so unoccluded that one may initially wonder if there is a proper seal. This ensures hours of comfortable listening, made possible by 64 Audio’s patented technology.

Being a 64 Audio product demands adherence to strict standards of accuracy, musicality, and balance while also offering something unique enough to earn a place among their legendary lineup of UIEMs. The scale to which Solo fulfills this is magnified by the fact that it employs a completely new speaker technology for 64 Audio, achieving it all with a single driver per side.

The agile performance expected of a planar driver achieves maximum realism by extracting subtle details in the music. These transients emerge from the mix, seamlessly keeping pace with the listener’s focus on the primary elements of the song. 64 Audio’s acoustic notch filters are strategically placed to eliminate sharpness without compromising driver performance. Apex core assists the high-mid and high frequencies in creating a vast sonic landscape, even in very complex mixes. Alongside this realism comes a tactile immersion in the textures of instruments and even the sonic characteristics of the recording equipment used in favorite tracks. By intentionally shaping the overall response of Solo, 64 Audio achieves a bass that has substantial impact and deep sub-bass presence.

Solo is being paired with 64 Audio's first pure copper cable. The OCC Copper, which is 23 x 25 AWG Wires, is built into eight-braids with a pleasant tactile feel as well as an impressively low 0.26Ω impedance rating. Solo comes standard with two of these cables:one 3.5mm single-ended and one balanced 4.4mm.